1. Field of the Invention
The present invention relates to a developing apparatus used for pieces of image forming apparatus such as a copying machine and a printer utilizing an electrophotographic or electrostatic recording method in which an image is formed by developing an electrostatic image formed in an image bearing member with a developer.
2. Related Background Art
Conventionally a two-component developer mainly containing toner particles (toner) and carrier particles (carrier) is widely used for the developing apparatus included in the electrophotographic or electrostatic recording type image forming apparatus. Particularly, in the color image forming apparatus forming a full-color or multi-color image, the two-component developer is used in almost all of the pieces of developing apparatus.
As is well known, toner density of the two-component developer, i.e., a ratio of a toner weight to the total weights of the carrier and the toner (TD ratio) is an extremely valuable factor in stabilizing image quality. The two-component developer toner is consumed during development, and the toner density is changed. Therefore, the color image forming apparatus is provided with developer density detection means for detecting the toner density of the two-component developer accommodated in a developing container of the developing apparatus (developing apparatus main body) and control means for replenishing, the toner to the developing container according to a detected signal. Thus, usually a developer density control apparatus is provided in the color image forming apparatus to keep the toner density of the two-component developer constant.
A replenishment agent (generally toner) whose replenishment amount is controlled by the control means from a replenish aperture into the developing container through a replenishment agent supply path (toner replenishing path). The replenish aperture is a connection portion between the replenishment agent supply path and the developing container. Then, the replenishment agent is stirred and mixed with a conveyance member (usually screw) such that the toner density of the two-component developer becomes substantially uniform. The conveyance member is provided in the developing container.
In the pieces of conventional developing apparatus disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2004-151586, JP-A No. 2004-133339, and JP-A No. 2003-84555, as shown in FIGS. 11 and 12, usually a falling and conveyance direction of the replenishment agent is a perpendicular direction in the replenish aperture. That is, conventionally the replenishment agent usually enters a developer containing part of the developing container while falling from the replenishment agent supply path and the replenishment agent goes down on a developer surface on the conveyance member in the developer containing part.
In a configuration in which a replenishment agent supply direction is perpendicular to the replenish aperture, namely, in the configuration in which the replenish aperture is located directly above the conveyance member in the developer containing part and the replenishment agent reaches the developer surface on the conveyance member while falling, there is the following problem. For example, when the full-color image forming apparatus provides for further multi colors (at least five colors) such as six colors while conventionally the four-color developing apparatus for yellow, magenta, cyan, and black is usually provided, sometimes the replenishment agent supply path interferes with the adjacent developing apparatus.
Therefore, as shown in FIG. 1, (1) sometimes the replenishment agent supply path is arranged at a position shifted from directly above the conveyance member in the developer containing part to supply the replenishment agent through a slope extending from the replenish aperture located with an inclination above the conveyance member.
It is also thought that the developing apparatus is miniaturized to arrange the replenishment agent supply path directly above the conveyance member in the developer containing part However, the miniaturization of the developing apparatus leads to a decrease in developer amount in the developing apparatus. This means that a fluctuation in toner density of the developer is increased by the toner consumption during the image formation, and the fluctuation in toner density causes a fluctuation in image density or a fluctuation in tint. Therefore, usually it is preferable that the replenishment agent supply path interference problem is solved by a method other than the miniaturization of the developing apparatus.
Further, there is the method in which the degraded carrier is recovered in each small amount and the carrier is replenished by newly mixing the carrier in the replenishment agent for the recovered carrier, and thereby the trouble of developer exchange is avoided while performance of the carrier which is of a charge imparting agent is maintained to some extent. Recently the adoption of this method is increasing. In this case, (2) the carrier is supplied while mixed in the toner which is of the replenishment agent. With reference to the carrier replenishment method, the carrier may independently be replenished, and the replenish aperture dedicated to the carrier may be provided in order to independently replenish the carrier.
However, in the case of the adoption of (1) the method of replenishing the replenishment agent through the slope or (2) the configuration in which at least the carrier is contained in the replenishment agent, it is found that there is a fear that clogging of the replenishment agent is generated near the replenish aperture to disrupt the supply of the replenishment agent.
It is though that the clogging of the replenishment agent near the replenish aperture is generated by a mechanism described below but not limited to the following mechanism.
As shown in FIG. 13, near the replenish aperture, a marginal stream is generated in association with a developer conveyance flow S0 in the developer containing part in a replenishment portion A including a slope for controlling the replenishment agent conveyance (falling) direction. The marginal stream includes a marginal stream (S1) in which a part of the developer conveyance flow S0 enters the replenishment portion A to become the marginal stream and a marginal stream (S2) in which the replenishment agent is accelerated to become the marginal stream by flowing the developer conveyance flow S0.
The marginal streams collide with a wall surface (hereinafter referred to as downstream side wall surface) W of the replenishment portion A located on the downstream side in the developer conveyance direction in the developer containing part, and the marginal streams rebound toward the opposite direction to the developer conveyance flow (S3). The downstream side wall surface W faces the replenishment portion A. Hereinafter the developer rebounding from the downstream side wall surface W is referred to as rebound developer.
Sometimes the following problems are caused by the marginal streams:    (i) in the case of a shape in which the rebound developer is difficult to return into the developer containing part due to a gravity, the rebound developer is easy to stay within the replenishment portion A, and    (ii) when the rebound developer has a high carrier content, the amount of rebound developer is increased because the carrier having a rebound coefficient higher than that of the toner is increased in the marginal stream.
When at least one of these two kinds of phenomena (i) and (ii) becomes prominent, the replenishment agent supply path is gradually clogged up, and thee is a fear that the supply of the replenishment agent is blocked.
Therefore, it is necessary to avoid the interruption of the supply of the replenishment agent to the developer containing part without clogging the replenishment agent near the replenish aperture despite of (1) the conveyance (falling) direction of the replenishment agent from the replenish aperture or (2) the carrier content in the replenishment agent.